Performance advances in central processing units (CPUs) and graphics processing units (GPUs) used in various computing applications have led increasingly demanding power supply requirements. In some cases, the power requirements of high end desktop workstations are approaching the power limits of commonly available wall receptacles (e.g., 15 A at 120Vac in the United States). To deliver as much power as possible from this limited source to these high performance computing elements, efficiency of the power supply becomes critical. Additionally, with modern processing devices operating at relatively low voltages, high currents—sometimes in the 100s of amperes—may be required. These high currents can be detrimental to high efficiency, because even small DC resistances in the power supply path can dissipate significant power at such current levels.
The final stage power supply for a CPU or GPU is sometimes known as a voltage regulator module, or “VRM.” VRMs may be configured to take an input voltage level (for example, 5Vdc) and convert it to the lower level required on-chip by the processor (for example, approximately 1Vdc). Input voltage levels of 5Vdc have been used in many VRM applications because the 5V to 1V conversion ration can be easily implemented as a two phase or four phase buck converter. With increasing power levels, and the associated increasing current, this becomes impractical for the reasons mentioned above. Increasing the input voltage, for example to 12Vdc, can alleviate some of these issues. However, because the voltage conversion ratio of a buck converter is directly proportional to its duty cycle, an excessive number of phases may become required to supply the required power to the load. This excessive number of phases may be undesirable for a number of reasons, including increased cost (because of the large number of components), decreased efficiency (because of increased switching losses, which may be exacerbated by hard switching in a buck converter).
Thus, it would be desirable to provide a power converter topology suitable for VRM (and other applications) that allows for high power handling with high efficiency and reduced costs.